1. Field of the Invention
This invention pertains, in its most general sense, to a process for continuously coating elongated and continuous bodies with a suitable protective coating. In its most immediate sense, this invention pertains to a process for coating wire such as that which is used in winding coils, in armatures and the like, and to apparatus with which the process can be carried out.
2. Description of the Prior Art
Wires, particularly wires which are utilized in coils and in windings in rotating machinery, are conventionally insulated so that the coils and windings formed thereby will not short out between adjacent wire sections. Such insulated wires are conventionally referred to as lacquered wires.
In the prior art, lacquered wires are produced by dissolving suitable insulation into a light hydrocarbon binder such as cresol which serves as a solvent, in order to provide a lacquer which is of a suitable viscosity for coating the wire. After the wire has been coated with the lacquer so produced, it is necessary to evaporate the solvent by subjecting the coated wire to elevated temperatures, and it is further necessary to harden the lacquer after the solvent has been evaporated therefrom in order to impart the necessary mechanical characteristics and electrical insulation characteristics which are required for wires of this type.
When this method is utilized, toxic or poisonous gases are emitted during the evaporation and hardening stages of the wire, making the process environmentally polluting. Moreover, the evaporation process is, in and of itself, an energy-intensive one, independently of the energy consumed during the subsequent hardening process.
In Federal Republic of Germany Offenlegungsschrift No. 27 44 721, a pulverized coating is disclosed which can be used to coat many types of articles in order to provide a mechanically stable corrosion shield. This reference also indicates that a pulverized material may be applied to such an article by means of an electrostatic process. Such processes involve the utilization of a coating chamber in which the pulverized material is given a negative charge while the object to be coated is given a positive charge. As a result of the potential difference between the pulverized material and the object to be coated, the pulverized material is set into motion and attracted onto the surface of the article to be coated, forming a coating which may later be sintered and fused onto the article to form a protective coating which is mechanically stable. In such electrostatic coating processes the thickness of the coating is a function of the duration in which the article remains in the coating chamber.
Existing electrostatic coating machines which utilize this principle to coat articles with coatings such as that disclosed in the above-mentioned reference are unsuitable for use in connection with coating elongated and continuous elements such as wire. Even if the structure of such devices were to be modified in order to accommodate wire (a modification not as yet known), such devices would be unsuitable because tolerances in insulation thickness of lacquered wire must as a practical matter be held at least within.+-.10 micrometers, and preferably better. This type of close-tolerance manufacture is necessary in order to insure that the insulation coating on the wire has a sufficiently high resistance to high voltage so that apparatus in which the wire is installed will not be subject to shorting and will not exceed the dimensions which practice dictates to be necessary.
Finally, it would be desirable to utilize a continuous sintering and hardening process in order to allow a continuous manufacturing process to take place over days and weeks. Such processes depend upon the uniformity of the particle size of the pulverized material which is to be sintered and hardened.
Thus, it would be desirable to provide a method for manufacturing lacquered wire which would not pollute the atmosphere with toxic or poisonous fumes, which would not be as energy-intensive as prior art methods, which would produce lacquered wire with an adequately uniform insulation thickness, and which would utilize a continuous sintering and hardening process.